The option image-viewer
>
black-background
is not longer available in gThumb since the version 3.2.0: [1] [2]
version 3.2.0
-------------
* always use a dark background in the image viewer
version 3.1.1
-------------
* Image viewer: use dark background by default, and more neutral color instead of black
From ChangeLog
for version 3.2.0: [3]
2003-02-03 Paolo Bacchilega <[email protected]>
* src/gthumb.schemas:
* src/gthumb-window.c (window_new, pref_black_background_changed)
* src/fullscreen.c (fullscreen_stop, fullscreen_start): added a black_background option to always use a black background for the image viewer.
A possible way to change the background is to edit the source code and recompile. [4] But I'm not a so familiar with programming and unfortunately can't help with that.